Control of stage, decorative, or similar lighting apparatus



24 1 1 J. T. WOOD April 95 CUNTROL OF STAGE, DECORATIVE. 0R SIMILAR 2 Sheets-Sheet 1 LIGHTING APPARATUS Filed April 4, 1949 Jmea 7." Wabd 6y M5 fiarnev Apnl 24, 1951 J. T. WOOD 2,550,317

, CONTROL OF STAGE, DECORATIVE, OR SIMILAR LIGHTING APPARATUS Filed April 4, 1949 2 Sheets-Sheet 2 F/G.4B.

low/7761- @7726? 7714 0006 Patented Apr. 24, 1951 CONTROIPORSTAGE, DECORATIVE, ORi' SIMILAR g'LIGI-ITING APPARATUS James Templeton" Wood, London, England, as-

signor toThe Strand Electric and Engineering Company Limited; London; England, a British company:

. Application April i, 1949, Serial No.- 855404,

In.,Great Britain April 15, 19 48 Z CIaimSL (Cl. 315 -250) The present invention relates to stage, decorativeorsimilar lighting apparatus andin-pa-rticu lar tothe control of dimmers whereby the degree of brill'ianey of a lamp or bank of lamps is varied in more-or-less gradual fashion.

Hitherto such dimming effects have beensecured by; the use of dimmin resistances in series with the various'banks' of lamps and controlled by heavy-duty switchgeanbut, especially in the case'of extensive effects demanded in connection with modernstage lighting, such apparatusisjapt to become very costly, complicated, and cumbersome. Also it is frequentlydesiredthat it shall be possible to pre-set the dimming apparatus/so that its effect may be introduced at a given moment and its operation shall then proceedwith'out further attention. It'has, however, been found that in all but the smallest installations the-complications of the apparatus required toproduce such pre-set effects is prohibitive, Further, when the lighting is fed from polyphase mains, oflicial regulations require that the load shallqbe balanced as between the various phases and, especially seeing that the minimumdistance between apparatus connected to different phases is prescribed, difliculties which have hitherto proved virtually insurmountable, at least in connection with largeinstallations, have arisen'in complying with the ofiicialregulations. It is the main object of the present invention to overcome these variousdrawbacks and other difiiculties which have been encounteredandto provide an apparatus of the kind set forthof far greater simplicitythan that hitherto proposed. Further, control'independent of, the load up to the full limit of the power-handling capacity of-"th'e'ap'-' paratus is secured. Also, in the case cf polyphase supplies, not only is load balance: between the phases attained, but the voltageacrossthe-load can never exceed that'between onejphase and neutraha condition which overcomes the disad vantage arising from limitation of distance between items of apparatus ,mentionedabove;

According to the invention, in stage-lighting or analogous equipment thelighting; 'load is fed from an alternating-current[supply through one or more thermionic valves, each of which is provided in its grid circuit with controlling means whereby the loadtransmitted through th'e valve is regulated. In practice, thetype-of valve'ikhown as the thyratron, that is to say, a gas-'fill'dtriode, is found to bemost suitable for the purpose'of the invention. In the casein which a'supplyfis drawn from polyphase mains;- aacorresponding number :of valvesis used the most 'COIIHIIOIIilIl;

2., stance 'is,of course,- thatoffathree-phase supply in connection with which" three valves would be employed, the anodes being connected to therespective. phases andthe cathodes .toa common point constitutingone of the load terminals, the other. terminal of the load being connected'to' neutral conductor.

For the purpose of controllingpeach valve a system as described with reference to Figure l ofthe drawings accompanying thisspecification may be used; In this figure the voltage applied tothe anode is represented by the curve I, assumed to beapproximately of sine form. To the gridcircuit'of the valve there is connected an alternatingrcurrent supplyof thejsam-e frequency asthatof the supply to the. anodebut laggingby this 'beingrepresented in Figure l by. the volt-' age curve2. Thevalve isof such anature as to becomelconductivewhen the'voltage. on its anode is positive, the valve cutting off at the end of each half-cycle at which theanode ceases to become positive andbecomes-negative unless otherwise controlled by its grid. In the, case represented in Figure 1, the striking action due to the grid volt-, age represented by the curve 2 firstbecomes possible at. the instantrepresentedi at the point 3- at which theanode voltage. has dropped to zero and is about to become negative, thecorrespondingvoltage on the curve2 being then a maximum. Due to the approximatelysine form-of. the .curve 2, however, ifthe strikinglpoint can be caused to travel backwards from the maximum point 3to a point such as 5 the valvewill strike at an earlier point, such as v6, in theehalf-cycle, and the possibility. oftransmissionof power throughthe valve would be representedby theshaded area indicated on thecurve I. This effect is secured by'theinclusion in the grid circuit of.a.\D.- C. supply. in opposition ..to- -thepositive impulses of the. controlling ,voltagerepresentedlby the curve .2, and, by-varyingthis.opposing: D. C. voltage,- the-point onthe curvezatwhich the valvewill becaused to strike maymbealtered. By suitably-decreasing the D. C. voltage, therebyraising thecurvet2-to the position shown dotted, the. striking-action takes placeat the pointrepresented. at the point 5 on thecurve 2, that-is to say,- at the point B-on the anode Vvoltage .curve I I As an alternative method of control, instead of varying the D, C. voltage, the phase difierence between'the curves I and -2 might bealteredin order to secure the required travel of 'the points 5 and-,5along these-curves; or a combination of the abovernethods might :be-employed. Asrthe positivepeak of ,curvevlj should-@coincide initime with zero value of curve I, if either or both of these curves were so distorted that the peak is not midway between successive zero values, the phase diiference between the curves, apart from any regulating action, must be correspondingly varied from 90.

As in the case of a three-phase supply there is a valve with its controlling grid circuit in each phase, the total eifect as regards the anode circuit is represented in Figure 2, from which it will be seen that the load is balanced as between phases. It will be evident that if the point on the curve 2 were advanced to the negative maximum of that curve, the valve would conduct throughout the whole of the positive half-cycle. From this it would follow that, in the case of three-phase supply, two valves would be conducting at the same time, and, accordingly, means, as described below, is provided so that no two of the valves can be operative simultaneously, such a. contingency being undesirable as it would permit of an undue load current impulse. Thus, in the case of a three-phase supply, the conditions of maximum output of the regulating valves are depicted in Figure 3.

In order to allow for the possibility of presetting the apparatus so that, while it is carrying out a certain dimming operation, a further operation may be arranged for and subsequently put into action, whereupon its effect is carried out automatically, two or more sets of apparatus for supply of the above variable direct current may be provided, arrangements being made whereby, during the period that one such set is with each of such valves or sets of valves, two

or more sets of apparatus for the supply of variable direct current, and it is convenient to arrange such sets in two or more series or chains, means being provided for selectively connecting such chains to the main D. C. supply.

In effecting alteration in the conditions prevailing in one of the loads by switching the D. C. supply from one of the above chains to another in which a pre-setting operation has been effected, no change being desired in a given load, all that is necessary is to ensure that in respect of the latter load the pre-setting of the control apparatus in the second chain is the same as that in the first chain.

For a more complete understanding of the invention a diagrammatic representation of the essential features of a lay-out according to the present invention has been illustrated, by way of example, in Figure 4 of the drawings.

Referring to this figure, a three-phase supply whereof mains are indicated at A, B and. C has been assumed. It has also been assumed that the total number of lamps to be supplied has been divided into two loads 1 and 8, each having a set of thyratrons 9 and II! respectively. As indicated, the anodes of the thyratrons are connected respectivel to the phases A, B and C, the cathodes being connected to a common point constituting one of the terminals of the load, whereof the other terminal is connected to a neutral conductor H. For the purpose of impressing on the grids of the thyratrons an alternating-current supply of the same frequency as that applied to the anodes but lagging by an appropriate transformer TI is connected to the three-phase mains and serves to supply transformers T2 whereof the secondary windings are connected to the grids respectively through resistances R. Such an arrangement for securing displaced alternating-current supply is well known and requires no further description. For the sake of completeness, there is shown a transformer T3 serving to supply the valve filaments, the connections being indicated by the use of the reference letters X and Y.

Direct current for control purposes is introduced into the grid circuit by a conductor I! or [3, as the case may be, connected to the star point of the secondary windings of the transformers T2. The D. C. supply is obtained from mains l4 appropriately furnished from any suitable source, such, for instance, as a rectifier actuated from the alternating-current mains. In respect of each of the loads 1 and 8 there is provided apparatus for supplying variable direct current via the lead l2 or l3, as the case may be, such apparatus being, in the example illus trated, duplicated for the purpose above specified. For convenience of description these sets of apparatus will be referred to as the first and the second set respectively, and it will be noted that in respect of each load the first set is connected between supply leads I5 and I6, and the second set between leads I! and I8. Thus the various first sets corresponding to the different loads constitute a series or chain and the second sets a further series or chain, means being provided for the connection of the D. C. mains to either of the chains and for a gradual change over from one chain to the other. Such means comprises a double-ganged potentiometer p and it will be appreciated that, in the position shown, D. C. power is connected to the leads I! and I8 but that both the leads l5 and I6 are joined to the positive pole. On the other hand, if the movable contacts of the ganged potentiometer are reversed, the leads I5 and IE will be excited and the leads I! and [8 will both become connected to the positive pole. The leads I 6 and I8 are connected to the neutral lead I l; the voltage drop across the load, which is connected be tween neutral and the cathodes, is thus also used to oppose the voltage supplied by the transformer T2, and since from the characteristics of the valve employed, when once the valve is conducting, an alteration of grid voltage has no effect, this voltage will not affect the valve which is conducting but will prevent the succeeding valve from striking before the first has cut off. It will be seen by referring to Figure 3 that, under normal conditions, there is no voltage developed across the load immediately prior to the operation of each valve.

In respect to each chain, there is connected across the supply leads l5 and IE, or I! and 18, as the case may be, a potentiometer P or P. There are also switches S or S arranged to connect one of two leads l9, 2|! either to the lead l5 or IT or to the potentiometer P or P. These items of apparatus are for the purpose of controlling the voltage applied to the respective chains, the potentiometer P or P giving a gradual increase or decrease and corresponding to a master control in the normal form of switchboard, and the switches S or S providing the immediate maximum voltage as in the case of a master. on" or oil switch.

As the apparatus for supplying variable D. C, to each of the loads is precisely similar, that associated with the load I only will be described. The first set of such apparatus comprises a potentiometer Pl adapted, by means of a switch SI to be connected either to the leads l5 and 16 or to the leads l9 and I6, thereby operating alternatively directly from the potentiometer p or through the potentiometer P. The potentiometer Pl feeds direct current through a comparatively high resistance Rl to the lead I2, communicating with the grid circuits of the thyratrons 9, a switch S l however being interposed, whereby the supply lead l5 may be connected directly to the resistance RI, thus preventing the valves from conducting. The second set of D. C. control apparatus associated with the load I is precisely similar to the first set, comprising switches Sl S l, potentiometer Pl and resistance R I, the last-mentioned item being, as indicated, also connected to the lead l2. Similarly the sets of D. C. control apparatus associated with the lead [3 appertaining to the load 8 comprise respectively switches S2, S2, potentiometer P2 and resistance R2, and switches S'2, SZ', potentiometer P2 and resist-- ance R2.

By way of indicating the mode of functioning of the apparatus, attention will now be drawn to effects which would result from the setting indicated of the various items whereby direct current is supplied for controlling the load transmitted through the thyratrons, a D. C. supply of 100 volts being assumed. Considering first the D. C. controlling apparatus associated with the load 1, as regards the application by means of the potentiometers PI and P! respectively to the resistances RI and R I, it will be appreciated that the position of the sliding potentiometer contacts shown is the maximum in respect of PI and the minimum as regards P'I. Neglecting the current in the grid circuit, it will be seen that the lead l2, that is to say the junction of the resistances RI and R I, will be at cathode potential inasmuch as the potentiometer p is in such a position that full voltageis being applied across the leads I7 and I8. On moving the contacts of potentiometer p to their other extreme position, the potential across the leads I1 and I8 is gradually altered to that of the cathode and full voltage is applied across the leads I5 and IS, with the result that the lead 12 will have a potential of 50 volts negative with respect to the cathode.

Considering now the D. C. control apparatus associated with the load 8, seeing that in the case of each of the potentiometers P2 and P2 the sliding contact is at the mid point, when the potentiometer p is in the position drawn, both ends of the potentiometer P2 will be at cathode potential, and, on account of the high Value of the resistance R2, the mid point may be regarded as also at cathode potential. The mid point of the potentiometer P2, however, will be at a potential of 50 volts negative with respect to the cathode, and the lead I3, that is to say, the junction of the resistances R2 and RZ, will have a potential of 25 volts negative. If now the potentiometer in be adjusted so that 25 volts appear across the potentiometer P2 and '75 volts across P2, the mid points of these potentiometers will be respectively at 12.5 and 37.5 volts negative with respect to the cath ode, the lead I3 remaining at 25 volts. In other words, the potentiometers P and P2 being at midpoint adjustment, this latter voltage remains constant whatever the adjustment of the potentiometer 1). Similarly it can be shown that, when the moving contacts on the potentiometers P2 and P2 are set at different positions, the time taken for the output voltage change from one value to the other is that required for traversing the moving contacts of the potentiometer p from one extreme to the other. Moreover, the various adjustable items in the chain which, for the time being, is de-energized, may be actuated without affecting the output from the various sets of apparatus in the chain which is connected to the D. C. supply.

What I claim and desire to secure by Letters Patent of the United States is:

1. Apparatus for the control of stage, decorative and similar lighting devices fed with unidirectional current from a polyphase alternatingcurrent supply, comprising in combination thermionic valves of the same number as that of the phases of the supply, a lead from each of said valves connecting its anode circuit in series with the lighting load, a single source of direct-current supply, a double-ganged potentiometer connected across said direct-current supply, two sets of apparatus, each set including two pressure leads whereof one of said leads is connected to one pole of said direct-current supply and the remaining pressure leads of the two sets are connected respectively to the two sliders of said double-ganged potentiometer, a potentiometer connected across the pressure leads of each of said sets of apparatus, two resistances connected in series between the sliders of the last mentioned potentiometers, and a lead from the junction of said resistances to the grid circuit of each of said valves.

2. Apparatus for the control of stage, decorative and similar lighting devices fed with unidirectional current from a polyphase alternatingcurrent supply, the said lighting load being divided into at least two sections, comprising in respect of each section the combination of thermionic valves of the same number as that of the phases of the supply, a lead from each of said valves connecting its anode circuit in series with said lighting load section, a single source of direct-current supply, a double ganged potentiometer connected across said direct-current supply, two sets of apparatus in respect of each lighting load section, each set including two pressure leads whereof one of said leads is connected to one pole of said direct-current supply and the remaining pressure leads of the two sets are connected respectively to the two sliders of said double-ganged potentiometer, a potentiometer connected across the pressure leads of each of said sets of apparatus, two resistances connected in series between the sliders of the last mentioned potentiometers, and a lead from the junction of said resistances to the grid circuit of each of said valves appertaining to said lighting load section.

JAMES TEMPLETON WOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,190,757 Moyer Feb. 20, 1940 2,242,105 Brettel, Jr May 13, 1941 2,278,211 Moyer Mar. 31, 1942 2,366,537 Livingston Jan. 2, 1945 

